Why Cleaner fish punish their partners for putting on weight

Largest fish in harem will turn into rival male

June 2011: Telling your partner to watch her weight is not recommended - unless you're a male cleaner fish, reports a new study.

Cleaner fish feed in male-female pairs by removing parasites from larger ‘client' fish. While providing this cleaning service, cleaners may get greedy and bite clients rather than sticking to parasites. This cheating by cleaners causes mealtimes to come to an abrupt end as the irritated client fish swims off.

RICH PICKINGS: Cleaner fish remove parasites from larger fish - but are not averse to sometimes taking a bigger bite. Picture: Joao Paulo Krajewski

But it's not just the client fish that is disgruntled. Females males that bite clients receive aggressive punishment from their male partners for such greedy behaviour. And with good reason.

Greedy females kept in check with harsh punishments
Scientists from the Zoological Society of London (ZSL) and a number of other leading scientific institutions have now shown that male fish lose more than just a meal from their partner's big appetite - they also risk the female becoming so large that she will turn into a rival male.

Cleaner fish live in groups led by one dominant male with a harem of up to 16 females. All cleaner fish are born female and turn into males when they become the biggest fish in their group. A male cleaner fish usually partners with the biggest female fish in the harem for cleaning duties.

‘Our research shows that male cleaner fish are sensitive to their female partner's size. One reason for keeping a cheating female in check may be to stop her eating too much and then challenging his position as the dominant male on the reef,' says Dr Nichola Raihani, lead author from ZSL.

Deterrent alters the female's behaviour
The research also shows that the male cleaner fish distinguish between high and low value meals and will punish the female more severely if she drives off a high-value client.

The female fish will respond to this punishment by providing better service to high value clients in the future. This is the first non-human example of where punishment fits the crime and results in the offender adjusting their behaviour according to the potential penalties.

Dr Nichola Raihani says: ‘Cleaner fish and humans may not share many physical traits, but cleaner fish punish cheating individuals, just as we punish people who step outside of the law. In both situations, harsher punishment may serve as a stronger deterrent against future crimes.'

http://www.wildlifeextra.com/go/news/cleaner-fish2011.html

Tropical fish are mammal-like parents

Discus fish are surprisingly attentive parents, scientists have found.


The colourful little creatures are known to feed their offspring with a nutritious mucus on their skin.

Now a study has suggested that the tropical fish actually wean their fry, "encouraging" them to forage for themselves, and that when it comes to looking after their young, discus fish have more in common with mammals.

Researchers describe their behaviour in the Journal of Experimental Biology.

This nurturing in discus fish is a well recognised behaviour, but this is the first time it has been studied in detail.

Intensive caring
Mr Jonathan Buckley from the University of Plymouth, UK, was a member of the team that carried out the study.

Along with his supervisor, Dr Katherine Sloman, and colleagues in Brazil, he found that, when it comes to looking after their young, discus fish have more in common with mammals than with most other fish.

He explained: "For the first couple of weeks - when the fry first hatch - the parents take amazingly good care of them."


Both parents' skin is covered in the mucus; the offspring surround the parent and constantly nibble on it.

At this stage, the tiny, vulnerable fry are never on their own. The male and female even share parental responsibility - "flicking" the young from one parent to the other when they need a break from feeding them.

Mr Buckley likened this to mammals suckling their young.

He and his team have now documented some even more striking similarities between the way these fish take care of their fry and the way mammals nurture and feed their babies.

He told BBC News that, after the first two weeks, the parents appeared to deliberately wean their young.

"In week three there's a change - the parents are constantly swimming away," he explained.

"We think this is the beginning of the weaning period - they're trying to make it more energetically efficient for the fry to forage rather than feed."

When the researchers studied the mucus itself, they found that it contained antibodies - immune system-bolstering substances.

"This transfer of antibodies to offspring is primarily a staple of mammalian parental care and [previously] unseen in fish," he said.

Parents share responsibility for their fry

These findings show, Mr Buckley added, just how much fish are underestimated in terms of the complexity of their behaviour.

The work could also show how the fish might be affected by pollution in their Amazon habitat.

Pollutants, particularly from mining, run into the waters and the scientists think that these could be absorbed into the mucus and, subsequently fed to the fry.

"The capture and sale of this species generates a significant amount of money for the people who live in that part of Brazil," Mr Buckley said.

"So it's important to understand how the fish are affected by changes in their environment."

Dr Sloman collaborated with Adalberto Val from the Laboratory of Ecophysiology and Molecular Evolution in Manaus, Brazil, to set up the colony of breeding discus fish that were used in this study.


By Victoria Gill

Science and nature reporter, BBC News

Tropical fish are mammal-like parents

Discus fish are surprisingly attentive parents, scientists have found.


The colourful little creatures are known to feed their offspring with a nutritious mucus on their skin.

Now a study has suggested that the tropical fish actually wean their fry, "encouraging" them to forage for themselves, and that when it comes to looking after their young, discus fish have more in common with mammals.

Researchers describe their behaviour in the Journal of Experimental Biology.

This nurturing in discus fish is a well recognised behaviour, but this is the first time it has been studied in detail.

Intensive caring
Mr Jonathan Buckley from the University of Plymouth, UK, was a member of the team that carried out the study.

Along with his supervisor, Dr Katherine Sloman, and colleagues in Brazil, he found that, when it comes to looking after their young, discus fish have more in common with mammals than with most other fish.

He explained: "For the first couple of weeks - when the fry first hatch - the parents take amazingly good care of them."


Both parents' skin is covered in the mucus; the offspring surround the parent and constantly nibble on it.

At this stage, the tiny, vulnerable fry are never on their own. The male and female even share parental responsibility - "flicking" the young from one parent to the other when they need a break from feeding them.

Mr Buckley likened this to mammals suckling their young.

He and his team have now documented some even more striking similarities between the way these fish take care of their fry and the way mammals nurture and feed their babies.

He told BBC News that, after the first two weeks, the parents appeared to deliberately wean their young.

"In week three there's a change - the parents are constantly swimming away," he explained.

"We think this is the beginning of the weaning period - they're trying to make it more energetically efficient for the fry to forage rather than feed."

When the researchers studied the mucus itself, they found that it contained antibodies - immune system-bolstering substances.

"This transfer of antibodies to offspring is primarily a staple of mammalian parental care and [previously] unseen in fish," he said.

Parents share responsibility for their fry

These findings show, Mr Buckley added, just how much fish are underestimated in terms of the complexity of their behaviour.

The work could also show how the fish might be affected by pollution in their Amazon habitat.

Pollutants, particularly from mining, run into the waters and the scientists think that these could be absorbed into the mucus and, subsequently fed to the fry.

"The capture and sale of this species generates a significant amount of money for the people who live in that part of Brazil," Mr Buckley said.

"So it's important to understand how the fish are affected by changes in their environment."

Dr Sloman collaborated with Adalberto Val from the Laboratory of Ecophysiology and Molecular Evolution in Manaus, Brazil, to set up the colony of breeding discus fish that were used in this study.


By Victoria Gill

Science and nature reporter, BBC News